Set Pattern — the computer actually makes no decisions; all enemies will make the same moves every time regardless of what the player does. Most of the enemies in Super Mario Bros. fit this category.

AI Roulette — again, the computer is not making decisions per se; it is simply choosing a move at random. This type is often seen in turn-based Roleplaying Games.

Analytical, or Responsive — the computer chooses a move based on the situation; the ghosts in Pac-Man fall into this category, which in 1980 was considered impressive.

It is in this third group that Artificial Stupidity can be found. AS is when the AI can select a move for its character(s), and consistently chooses ones that are completely stupid. While it is very rarely included on purpose as a balancing factor, such as to balance out the fact that The Computer Is a Cheating Bastard, Artificial Stupidity is often a result of poor programming; the programmers simply didn't program the AI not to make that move, and when the AI evaluates its choices, the poor move looks like the best one. (It's far more likely that The Computer Is a Cheating Bastard will be introduced to compensate for Artificial Stupidity rather than the other way round.)

Artificial Stupidity is particularly visible in Role Playing Games, be they turn-based games like the majority of the Final Fantasy and Dragon Quest series, or strategy-based games like Final Fantasy Tactics and Disgaea, simply because it is in these types of games that the decision-making process is the most important, and therefore, the most visible. It can potentially exist in any game involving an analytical or responsive AI, though, and the more analytical the game, the easier it is to get an AI that's, well, stupid. For instance, even good chess games can suffer from a version of this, called the "horizon effect".

Differs from AI Roulette because AI Roulette chooses moves randomly. Artificial Stupidity puts some "thought" in its moves, making the most obvious stupidities less likely but creating more consistent general incompetence. See also AI Breaker for exploiting these.

Suicidal Overconfidence is a specific case of this that's usually less about bad programming or making the game easier than about allowing the player to have something to do.

Note that, for the sake of argument, this trope typically only covers situations that a player can be reasonably expected to enter over the course of normal gameplay. It's hardly fair to blame the programmers, after all, if you use a cheat device to get special weapons ahead of time and the AI has no idea what's going on.